Re: [Xen-devel] [PATCH v2] x86/apicv: fix RTC periodic timer and apicv issue

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Xuquan (Quan Xu) [mailto:xuquan8@xxxxxxxxxx]
> Sent: Monday, October 17, 2016 5:28 PM
> 
> >>
> >>Back to the main open before holiday - multiple EOIs may come to clear
> >>irq_issued before guest actually handles the very vpt injection
> >>(possible if vpt vector is shared with other sources). I don't see a
> >>good solution on that open... :/
> >>
> >>We've discussed various options which all fail in one or another place
> >>- either miss an injection, or incur undesired injections.
> >>Possibly we should consider another direction - fall back to non-apicv
> >>path when we see vpt vector pending but it's not the highest one.
> >>
> >>Original condition to enter virtual intr delivery:
> >>        else if ( cpu_has_vmx_virtual_intr_delivery &&
> >>              intack.source != hvm_intsrc_pic &&
> >>              intack.source != hvm_intsrc_vector )
> >>
> >>now new condition:
> >>        else if ( cpu_has_vmx_virtual_intr_delivery &&
> >>              intack.source != hvm_intsrc_pic &&
> >>              intack.source != hvm_intsrc_vector &&
> >>                    (pt_vector == -1 || intack.vector == pt_vector) )
> >>
> >>Thoughts?
> >>
> >Kevin,
> >When I try to fix it as your suggestion, I cannot boot the guest, with below
> >message(from xl dmesg):
> 
> with Kevin's patch, the hypervisor always calls ' vmx_inject_extint() ->
> __vmx_inject_exception()' to inject exception, then vm-entry on loop..
> the interrupt (PT or IPI, or others) can't deliver to guest..
> 
> and so far, we suppress MSR-based APIC suggestion when having APIC-V by
> http://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=7f2e992b824ec62a2818e643
> 90ac2ccfbd74e6b7
> so I think we couldn't fallback to non-apicv dynamically here..
> 

What about setting EOI exit bitmap for intack.vector when it's higher
than pending pt_vector? This way we can guarantee there's always a
chance to post pt_vector when pt_vector becomes the highest one...

(of course you need make later pt_intr_post conditionally then, only
when intack.vector==pt_vector)

Thanks
Kevin

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